1. Field of the Invention
The present invention relates to a configuration for a circuit for processing video and audio signals.
2. Description of the Related Art
Broadcasting technologies and video- and audio-related signal encoding technologies have recently been advanced remarkably. In the telecasting field, for example, not just conventional broadcasts at a standard resolution but also so-called “Hi-Vision” broadcasts with a higher video quality have already been brought to general home users. In the field of data compression on the other hand, MPEG-2 and MPEG-4 standards were fixed so that video and audio data can be freely read from, or written on, a storage medium such as a DVD in compliance with those standards.
To make such a drive even more convenient for the users, the drive preferably has the capability of processing multiple types of signals, complying with mutually different sets of standards, by itself. Furthermore, if all necessary components of such a drive could be integrated together on a single chip, the design process of such a drive should be carried out smoothly. Unfortunately, though, the greater the number of types of signals to be processed, the more complicated the signal processor becomes and the more difficult it is to integrate all necessary components together on a single chip.
Thus, in many cases, a number of dedicated processors (blocks) are provided independently to process new types of signals quickly enough. For example, Japanese Laid-Open Publication No. 2-154583 discloses a technique of providing signal processors for two types of analog TV signals (i.e., the standard resolution signal and the Hi-Vision signal), respectively. An optical disc drive to process digital signals is also provided with a plurality of signal processors for processing signals complying with a number of data compression standards (such as the MPEG-2 and MPEG-4 standards). Hereinafter, a more specific circuit configuration will be described.
FIG. 1 shows a configuration for an analog broadcast signal demodulator 10. This demodulator 10 is supposed to be built in a TV set and have the function of processing a Hi-Vision broadcast signal complying with the MUSE standards (which will be referred to herein as an “MUSE signal”) and a standard resolution signal complying with the NTSC standard (which will be referred to herein as an “NTSC signal”) and outputting the processed signals to a display and loudspeakers. These signals may be received at the same time. However, usually one of the two signals is selectively processed by a tuner (not shown) according to the user's choice (i.e., tuning). Each of these signals includes an audio signal.
If the MUSE signal has been selected, then the MUSE signal is received at an input terminal 1. A video/audio processor 2 extracts video- and audio-related signals from the MUSE signal, demodulates these signals into audible and visible formats and then outputs them as video and audio signals. On the other hand, if the NTSC signal has been selected, then the NTSC signal is received at an input terminal 7. A video/audio processor 8 also extracts video- and audio-related signals from the NTSC signal, demodulates these signals into audible and visible formats and then outputs them as video and audio signals. The signals obtained from the MUSE signal are digital data. Thus, the processing performed by the video/audio processor 2 is done on that digital data. On the other hand, the signals obtained from the NTSC signal are analog data. Thus, the processing performed by the video/audio processor 8 is done on that analog data. The specific contents of these two types of processing are different from each other but the description thereof will be omitted herein because those contents have little importance.
Synchronously with the selection of the MUSE signal or the NTSC signal, a video switch 3 and an audio switch 5 choose the signal paths. Specifically, when the MUSE signal is selected, the video and audio switches 3 and 5 connect the video/audio processor 2 to a video signal output terminal 4 and an audio signal output terminal 6. Meanwhile, when the NTSC signal is selected, the video and audio switches 3 and 5 connect the video/audio processor 8 to the video signal output terminal 4 and the audio signal output terminal 6. In this manner, the video and audio signals, which have been demodulated from the broadcast signal selected, can be output through the output terminals 4 and 6, respectively.
On the other hand, FIG. 2 shows a configuration for a digital signal decoder 20. The decoder 20 is built in an optical disc drive, for example, decodes digital signals complying with two different sets of standards, and outputs resultant video and audio signals to a display and loudspeakers, respectively. In this example, the digital signals are an MPEG-2 program stream (which will be referred to herein as a “PS”) and an MPEG-2 transport stream (which will be referred to herein as a “TS”). For example, if a DVD is loaded as a given optical disc, the decoder 20 receives a PS. But if a Blu-ray Disc (BD) is loaded, then the decoder 20 receives a TS.
In this decoder 20, a PS is supplied to, and decoded by, a processing block 21a, while a TS is supplied to, and decoded by, a processing block 21b. It will be described how the PS is decoded by the processing block 21a. First, a video/audio decoder 22a extracts video data and audio data from the PS, decodes them, and then outputs the decoded data as a video signal and an audio signal. In this process, a clock signal CLK(a) having a frequency required for the PS processing is supplied from a clock generator 23a to the video/audio decoder 22a. The resultant video signal is passed to a resolution converter 24a, while the resultant audio signal is passed to an audio switch 28. The resolution converter 24a performs resolution conversion processing, including data decimation, interpolation and telecine conversion, on the video signal received and outputs the processed video signal to a video switch 26.
The video signal and audio signal, which are output from the processing block 21a, are both non-compressed digital signals and have discrete values. The video switch 26 operates in response to the clock signal CLK(a) supplied from the clock generator 23a. Likewise, the audio switch 28 also operates in response to a clock signal. However, the audio signal processing clock pulses are different from the video signal processing clock pulses. Thus, an audio processing clock generator 25a generates an audio signal processing clock signal from the clock signal CLK(a) and supplies it to the audio switch 28.
The processing block 21b performs decoding processing on the TS in a similar procedure. The video/audio decoder 22b, clock generator 23b, resolution converter 24b and audio processing clock generator 25b of the processing block 21b have the same functions as the counterparts of the identical names as already described for the PS processing block 21a except that the processing and setting of those components are adapted to the TS, and the description thereof will be omitted herein. The video and audio signals output from the processing block 21b are non-compressed digital signals, too. Accordingly, not only the video and audio signals but also a video processing clock signal CLK(b) and an audio processing clock signal are output to the video switch 26 and audio switch 28.
The video switch 26 and audio switch 28 choose signal paths, thereby passing the video and audio signals, supplied from either the processing block 21a or the processing block 21b, to a video DAC 27 and an audio DAC 28, respectively. As a result, those digital signals are converted into analog signals and then output to an external TV set and loudspeakers, for example.
Both the analog broadcast signal demodulator 10 shown in FIG. 1 and the decoder 20 shown in FIG. 2 perform two different types of processing and change the outputs via switches according to the type of the input signal just before the processed data are eventually output. In the analog broadcast signal demodulator 10, the target of the demodulation processing is divided into digital data and analog data, and therefore, there is no choice but processing the two types of data separately until those data are eventually output.
However, if the targets of processing are two similar types of MPEG-2 based digital signals like the PS and TS, then the decoder 20 will perform technically analogous processing on both of the two signals, which causes various problems.
Firstly, two processing blocks need to be provided for the two different types of signals to be processed, thus requiring an increased number of redundant components. In the decoder 20, for example, two resolution converters 24a and 24b of the same type need to be provided. Then, the processing block of each signal should have an increased circuit scale. Consequently, the production cost rises and the power dissipation increases, too.
Secondly, if two different types of clock signals are needed for two different signals to be processed, then lines to transmit those clock signals must be extended a long distance to some components that are located next to their output terminals (e.g., the switches 26 and 28 in the example illustrated in FIG. 2). However, those extended lines would constitute big obstacles in laying out the other circuit components during a design process. Furthermore, such long transmission lines should increase unnecessary radiation within the circuit, too.
Thirdly, the conventional circuit selectively outputs just one of the two types of signals via the switches, and therefore cannot present a video using multiple types of signals (e.g., a thumbnail display or a picture-in-picture display). For that purpose, another processor is needed, thus increasing the circuit size, too.